Solubilization of porcine zonae pellucidae by trypsin and pronase

The porcine zona pellucida was dissolved with difficulty by trypsin in isotonic solution, whereas it was efficiently dissolved by pronase. A structural change of the zona was induced in hypotonic solution, resulting in acceleration of dissolution by these proteases. The solubilization rate of three families (PZP1-3) of zona protein by both enzymes was analyzed by HPLC. In hypotonic solution, PZP1 was solubilized first, followed by PZP2; and PZP3 was then finally released. In isotonic solution, PZP1 and PZP2 were also solubilized faster than PZP3, which was almost completely resistant to trypsin, showing that the solubilization of the zona depended on that of PZP3. Noticeably, high molecular weight products were produced as the proteolytic hydrolysis proceeded in PBS. Circular dichroic spectra and electrophoretograms of the tryptic hydrolysates showed that the zona may have a regular supramolecular structure.